1. Field of the Invention
The instant invention relates generally to industrial fabrics. More particularly, the invention relates to a replacement for conventional weaving of substrates and fabrics for endless or seamed industrial fabrics, such as those used in the forming, pressing and dryer sections of a papermaking machine. The invention, however, can also be applied to industrial fabrics used in applications other than papermaking.
2. Background of the Invention
During the papermaking process, a cellulosic fibrous web is formed by depositing a fibrous slurry, that is, an aqueous dispersion of cellulose fibers, onto a moving forming fabric in the forming section of a papermaking machine. A large amount of water is drained from the slurry through the forming fabric, leaving the cellulosic fibrous web on the surface of the forming fabric.
The newly formed cellulosic fibrous web proceeds from the forming section to a press section that includes a series of press nips. The cellulosic fibrous web passes through the press nips supported by a press fabric, or, as is often the case, between two such press fabrics. In the press nips, the cellulosic fibrous web is subjected to compressive forces which squeeze water therefrom, and which adhere the cellulosic fibers in the web to one another to turn the cellulosic fibrous web into a paper sheet. The water is accepted by the press fabric or fabrics and, ideally, does not return to the paper sheet.
The paper sheet finally proceeds to a dryer section, which includes at least one series of rotatable dryer drums or cylinders, which are internally heated by steam. The newly formed paper sheet is sequentially directed in a serpentine path around each in the series of drums by a dryer fabric, which holds the paper sheet closely against the surfaces of the drums. The heated drums reduce the water content of the paper sheet to a desirable level through evaporation.
It should be appreciated that forming, press and dryer fabrics all take the form of endless loops on the papermaking machine and function in the manner of conveyors. It should further be appreciated that paper manufacture is a continuous process which proceeds at considerable speeds. That is to say, the fibrous slurry is continuously deposited onto the forming fabric in the forming section, while a newly manufactured paper sheet is continuously wound onto rolls after it exits from the dryer section.
The instant invention relates primarily to the press fabrics used in the press section of a papermaking, tissue or through-air drying (TAD) machine, but it may also find application in the forming and dryer sections of a papermaking, tissue or TAD machine, in which the fabrics are generally known as forming fabrics, dryer fabrics, and TAD fabrics as well as in those fabrics used as bases for polymer-coated paper industry process belts, such as, for example, long nip press belts.
Forming fabrics play a critical role during the papermaking process. One of their functions is to form and convey the product being manufactured from the forming section to the press section or next papermaking operation. Dryer fabrics play a critical role as well, transporting the paper product through the dryer section of the papermaking machine.
In addition, the instant invention may be used to construct corrugator belts used to manufacture corrugated paper board and engineered fabrics used in the production of wetlaid and drylaid pulp, in processes related to papermaking such as those using sludge filters and chemiwashers, and in the production of nonwovens produced by hydroentangling (wet process), meltblowing, spunbonding airlaid, or needle punching. Such fabrics and belts include, but are not limited to embossing, conveying, and support fabrics and belts used in processes for producing nonwoven products.
Contemporary fabrics are used in a wide variety of styles designed to meet the requirements of the papermaking machines on which they are installed for the paper grades being manufactured. Generally, they comprise a woven base fabric, which, depending on the application may include a needled batting of fine, nonwoven fibrous material. The base fabrics may be woven from monofilament, plied monofilament, multifilament or plied multifilament yarns, and may be single-layered, multi-layered or laminated. The yarns are typically extruded from any one of several synthetic polymeric resins, such as polyamide and polyester resins, used for this purpose by those of ordinary skill in the papermaking machine clothing arts.
Woven fabrics take many different forms. For example, they may be woven endless, or flat woven and subsequently rendered into endless form with a seam. Alternatively, they may be produced by a process commonly known as modified endless weaving, wherein the widthwise edges of the base fabric are provided with seaming loops using the machine direction (MD) yarns thereof. In this process, the MD yarns weave continuously back and forth between the widthwise edges of the fabric, at each edge turning back and forming a seaming loop. A base fabric produced in this fashion is placed into endless form during installation on a papermaking machine, and for this reason is referred to as an on-machine-seamable fabric. To place such a fabric into endless form, the two widthwise edges are seamed together by interdigitating the seaming loops at the two ends of the fabric, and by directing a so-called pin, or pintle, through the passage defined by the interdigitated seaming loops in order to lock the two ends of the fabric together.
Further, the woven base fabrics may be laminated by placing one base fabric within the endless loop formed by another, and in the case of press fabrics, by needling a staple fiber batt through both base fabrics to join them to each other. One or both woven base fabrics may be of the on-machine-seamable type.
In addition to woven fabrics, knitted fabrics have been used for paper machine clothing, such as for press fabric substrates that enables advantage to be taken of the inherent characteristics of a knitted fabric. Knitted fabrics are advantageous over woven fabrics for many reasons. In the production of a woven structure, the cost of production increases as the cloth width increases due to the reduction in weaving speed. For example, a loom on which a woven structure is produced can operate at and above 60 weft insertions per minute on cloths of 100 inches wide, whereas for cloths of 380 inches wide, the speed of weft insertions can be as low as 30 insertions per minute. In knitting, however, the production speed is largely independent of width, and production speeds are approximately eight times higher at 60 inches. Since a knitting machine results in a much higher production rate when compared to that of a weaving loom, knitted fabrics have a substantial cost advantage as compared with equivalent woven fabrics
For forming fabrics, which are flat woven and require a complex woven seam to create an endless fabric loop, use of knitted fabrics joined together as defined herein eliminate the need for costly seaming. Furthermore, the weave patterns for forming fabrics are limited to those which can be seamed to make the fabric endless. Also, for all fabrics, the flow passage of fluids, whether air, water or a combination thereof, are limited by the size of the yarns and weave patterns incorporated. Knits on the other hand introduce a greater degree of freedom in designing the fluid flow path geometry. Additionally, certain materials such as polyethylene naphthalene (PEN) have been desired as a high modulus yarn material to be used as the MD or load bearing yarns in a forming fabric. PEN, however, is easily abraded during the weaving process. PEN is also brittle and the resulting seam strength is usually low. Incorporating PEN as a MD member in a warp knit structure will allow use of this material and similar materials by overcoming the previously discussed inherent shortcomings of such materials.
In addition, in many cases in which a conventional woven structure is used, knuckles are formed on the yarn crossover points. These knuckles are susceptible to abrasive wear and can result in marking of the product being manufactured, and in the case of papermaking dryer fabrics and certain fabrics for the production of nonwoven products, can cause an excessive amount of entrained boundary layer air resulting in distortion of the product being produced. A knitted structure, however, can be designed to have a smoother sheet contact surface using the same material component yarns, while also having a higher flexural resistance and hence a longer service life.
In any event, fabrics and substrates can be in the form of endless loops, or can be seamable into such forms, having a specific length, measured longitudinally therearound, and a specific width, measured transversely thereacross. Because papermaking machine configurations vary widely, papermaking machine clothing manufacturers are required to produce forming, press and dryer fabrics, as well as other papermaking machine clothing, to the dimensions required to fit particular positions in the papermaking machines of their customers. Needless to say, this requirement makes it difficult to streamline the manufacturing process, as each fabric must typically be made to order.
Fabrics in modern papermaking machines may have a width of from 5 to over 33 feet, a length of from 40 to over 400 feet and weigh from approximately 100 to over 3,000 pounds. As would be expected, these fabrics wear out and require replacement. Replacement of fabrics often involves taking the machine out of service, removing the worn fabric, setting up to install a fabric and installing the new fabric.
In response to this need to produce fabrics in a variety of lengths and widths more quickly and more efficiently, subassembly of narrow width woven or nonwoven substrates into full width fabrics has become an established method of manufacturing for press fabrics. There are benefits in both the performance of the fabric due to its structure and in the efficiencies of manufacturing the fabric. A key requirement for subassembly of narrow width material strips into full size fabrics is to devise a joining method along the length of the substrate strips. Numerous methods have been employed including sewing, ultrasonic bonding and thermal bonding. In all cases, however, the resulting bond has two potential limitations: (1) the bond strength, measured as cross-machine direction (CD) breaking strength, is usually lower than that of the body of the strip itself; and (2) the joined area does not have exactly the same uniformity as the body of the strip, especially with respect to fluid flow, whether air or water, which results in the potential for objectionable marking of the paper product.
In press fabrics, a needled fiber batt structure compensates to a degree for these limitations. The key bond strength requirement in the subassembly of the press fabric is to enable handling of the substrate through the needling process. The MD strength in the final fabric comes from the yarns/monofilaments of the substrate, while the CD strength comes from the bond and the needled fiber batt. The batt also helps to mask the structural discontinuity at the MD oriented seam points in the subassembled narrow width strips, which would otherwise cause marking of or non-uniform water removal from the paper product being manufactured.
In response to the need to produce fabrics in a variety of lengths and widths more quickly and efficiently, fabrics and substrates have been produced using a spiral winding technique disclosed in commonly assigned U.S. Pat. No. 5,360,656 to Rexfelt et al., the contents of which are incorporated herein by reference.
U.S. Pat. No. 5,360,656 discloses a press fabric comprising a base fabric having one or more layers of staple fiber material needled thereinto. The base fabric comprises at least one layer composed of a spirally wound strip of woven fabric having a width which is smaller than the width of the base fabric. The base fabric is endless in the longitudinal, or machine direction. Lengthwise threads of the spirally wound strip make an angle with the longitudinal direction of the press fabric. The strip of woven fabric may be flat-woven on a loom that is narrower than those typically used in the production of papermaking machine clothing. A loom as narrow as 20 inches (0.5 meters) could be used to produce a woven fabric strip, but, for reasons of practicality, a conventional textile loom having a width of from 40 to 60 inches (1.0 to 1.5 meters) may be preferred.
The base fabric comprises a plurality of spirally wound and joined turns of the relatively narrow woven fabric strip. The fabric strip is woven from lengthwise (warp) and crosswise (filling) yarns. Adjacent turns of the spirally wound fabric strip may be abutted against one another, and the spirally continuous seam so produced may be closed by sewing, stitching, melting, welding (e.g. ultrasonic) or gluing. Alternatively, adjacent longitudinal edge portions of adjoining spiral turns may be arranged overlappingly, so long as the edges have a reduced thickness, so as not to give rise to an increased thickness in the area of the overlap. Alternatively still, the spacing between lengthwise yarns may be increased at the edges of the strip, so that, when adjoining spiral turns are arranged overlappingly, there may be an unchanged spacing between lengthwise threads in the area of the overlap.
In any case, a base fabric, taking the form of an endless loop and having an inner surface, a longitudinal (machine) direction and a transverse (cross-machine) direction, is the result. The lateral edges of the base fabric are then trimmed to render them parallel to its longitudinal (machine) direction. The angle between the machine direction of the base fabric and the spirally continuous seam may be relatively small, that is, typically less than 10-degrees. By the same token, the lengthwise (warp) yarns of the fabric strip make the same relatively small angle with the longitudinal (machine) direction of the base fabric. Similarly, the crosswise (filling) yarns of the fabric strip, being substantially perpendicular to the lengthwise (warp) yarns, make the same relatively small angle with the transverse (cross-machine) direction of the base fabric.
Commonly assigned U.S. patent application Ser. No. 10/364,145 filed Feb. 11, 2003 entitled “Unique Fabric Structure for Industrial Fabrics,” the contents of which are incorporated herein by reference, discloses an industrial process fabric that is endless or made endless with a seam in a machine direction. The industrial process fabric comprises at least one layer of spiral turns formed by a spirally-wound strip of material, where the strip of material has a width that is narrower than the width of the industrial process fabric. The material strip can either be woven, nonwoven, knitted or an array of MD or CD yarns. Each spiral turn abuts against or overlaps with those adjacent thereto and are attached to each other using a bonding technique such as ultrasonic bonding, adhesive bonding, bonding through a low melt material and bonding through the use of bondable yarns. In addition, the spirally-wound material strips may be joined by sewing the longitudinal edges to one another. When an industrial process fabric comprising at least two layers is required, with each layer having a plurality of spiral turns formed by the spirally-wound strip of material, the layers are joined to each other using one of the previously described bonding techniques.
U.S. Pat. No. 6,162,518 discloses a length of textile that is used as a papermaking machine cover. To form the machine cover, a textile strip is drawn from a transversely moving supply roll onto two spaced rollers. Since the supply roll is moving in a direction transverse to the rollers, the textile strip is helically wound onto the rollers. The helical winding results in a plurality of textile strips having longitudinal edges that abut up against each adjacent edge. The helical winding of the textile strip continues until a desired width fabric is achieved.
Each textile strip consists of transverse threads (structural threads), which when taken together form a transverse thread bundle, and longitudinal threads (structural threads), which when taken together form a longitudinal thread bunch. The transverse and longitudinal threads (structural threads) are joined to one another at their intersection points, for example by bonding, cementing or the like. The structural threads are preferably part of a fabric, knit, thread bunch or an insert within a film or the like. To join the adjacent textile strips, the transverse threads from each edge of the adjacent textile strips are interdigitated with one another. Once interdigitated, a connecting thread, parallel to the longitudinal direction, is then placed over the interdigitated transverse threads and bonded to the transverse threads using an ultrasonic bonding means. Adjacent textile strips are joined in a like manner until a desired width paper machine cover is achieved.
U.S. Pat. No. 5,268,076 discloses a spirally-wound papermaking machine belt especially for use as a press belt. The belt comprises a plurality of fiber-belt strips and support belt strips. The fiber-belt strips consist of a fiber web which may evince different fiber orientations, finenesses and fiber densities, whereas the support belt strips may evince different structures such as woven, knit, spun fiber web, foil and or strips of composite sheets of nonwoven filaments. In addition to supply rolls that include the fiber-belt strips and the support belt strips, the belt manufacturing device comprises a needling machine and two advance rollers rotating on horizontal shafts, positioned horizontally apart.
At the beginning of the manufacturing process, a first strip of belt-material (“forming strip”) is pulled onto the two advance rollers. This forming strip acts as support or a forming platform for the belt during the belt construction process. Mounted thereupon are the individual fiber-belt strips and support belt strips from the supply rolls. Once the fiber-belt strips and support belt strips are mounted, the two advance rollers and the forming strip are displaced in the direction of advance whereby the fiber-belt and support belt strips are withdrawn from the supply rolls onto the forming strip in a spirally wound manner. Simultaneously with the addition of the fiber-belt and support belt strips to the forming strip, the needling machine is actuated so that the individual belt strips are needled together such that the fibers of the fiber-belt strips penetrate the support belt strips.
The process continues until the belt has attained its desired width. Once the finished belt is removed from the advance rollers, the forming strip that was used to support the belt during the forming process is removed, resulting in a belt that is either finished or one in which further processing may be performed. The support belt strips into which fibers from the fiber-belt strips are needled may have various configurations, such as having longitudinal edges that partly overlap or longitudinal edges that do not overlap and instead abut up against one another. In all configurations, however, the fiber-belt strips and the support belt strips are attached to one another by needling.
Commonly assigned U.S. Pat. No. 5,713,399, the contents of which are incorporated herein by reference, shows an approach to forming and closing the spirally continuous seam in a fabric of this type. According to the disclosed method, the fabric strip has a lateral fringe along at least one lateral edge thereof, the lateral fringe being unbound ends of its crosswise yarns extending beyond the lateral edge. During the spiral winding of the fringed strip, the lateral fringe of a turn overlies or underlies an adjacent turn of the strip, the lateral edges of the adjacent turns abutting against one another. The spirally continuous seam so obtained is closed by ultrasonically welding or bonding the overlying or underlying lateral fringe to the fabric strip in an adjacent turn.
As disclosed in U.S. Pat. No. 6,124,015, a multi-layer industrial fabric is assembled from at least one segment comprising at least one woven or nonwoven ply, in which the joints utilize jointing yarns or structures. The jointing structures, which may be continuous or discontinuous, engage with and interlock with each other to provide a secure mating engagement at selected locations on the segment(s), making up the fabric. The planar surfaces forming the joints are in the plane of the finished fabric and are thus not edge-to-edge joints. The fabric structure is assembled by interlocking together as many segments as are needed, to provide the required finished industrial fabric. For some applications it is desirable to make the interlocked joint between the jointing structures more secure. Examples of how to make the interlocked joint more secure include adhesives, chemically reactive systems such as polyurethane, or in the alternative, an inert layer of nonwoven material may be inserted between the plies, such as a thin layer of fibrous batt. A web of hot melt adhesive may also be used. This process, however, still results in a joint between the lateral edges of the segments that were joined together, which as aforementioned is a weak point of the fabric.
In addition to the previously discussed joining methods used to join adjacent fabric strips along the length of a substrate, is a butt seam that can be found in the aforementioned U.S. Pat. No. 5,360,656. This seam is between adjacent strips of fabric and includes stitching. The seams, however, are not load bearing and are merely there to hold the strips together so that the “base” structures formed by these joined together strips can be handled through subsequent manufacturing processes such as needling.
In any structure that comprises spirally wound strips of material, the connecting seam between two adjacent strips is a critical part of the fabric since uniform paper quality, low marking and excellent runnability of the fabric require a seam which is as similar as possible to the rest of the fabric with respect to properties such as thickness, structure, strength, permeability, etc. It is therefore important that the seam connecting region between adjoining spirally wound strips of material of any workable fabric in operation, have the same permeability to water and air as the rest of the fabric, thereby preventing marking by the seam region on the product being manufactured. Despite the considerable technical obstacles presented by these requirements, it is highly desirable to develop spirally wound fabrics because of the types of structures that can be incorporated, such as knits.
As previously discussed, the connecting seam region strength in press fabrics formed by spirally winding strips of material may be increased with the addition of a needled fiber batt material; this, however, is not an option with forming and dryer fabrics, or any other “fabric” that does not employ a layer of needled batt fibers. In forming and dryer fabrics, the structure has no batting to mask the discontinuities which may result from joining narrow width substrates to make a full width product and the bond strengths of current joining methods would not be sufficient in and of themselves for the fabrics to maintain their structural integrity and run on current machines.
Therefore, a need exists to provide an alternative to current methods used to create full size industrial fabrics and substrates base structures for fabrics, where the fabrics and substrates are created in portions from narrow width knitted structures, resulting in an assembled fabric having a strong, virtually undetectable connecting means between adjacent spirally wound knitted strips of material.